#include<stdio.h>

int main() {
    int N;
    scanf_s("%d", &N);
    double sum = 0.0;
    int sign = 1;
    for (int i = 1;i <= N;i++) {
        sum += sign * (double)i / (2 * i - 1);
        sign *= -1;
    }
    printf("%.3f", sum);
    return 0;
}